Answer:
Solution given:
since Rosie walked 18 km INA first day.
so
first term[a]=18km
again
she walked 90% of what she walked the day before which means
common ratio decreasing
common ratio[r]90%=0.9
sum of 10th day
=?
no of term (n)=10
now
we have
![Sum_(10)=(a(r^(n)-1))/(r-1)](https://img.qammunity.org/2022/formulas/mathematics/high-school/3b686jn886i22vicz4ro9nbk3y60vw0udl.png)
substituting value:
=
![(18(0.9^(10)-1))/(0.9-1)](https://img.qammunity.org/2022/formulas/mathematics/high-school/h69sgptmb0v2t9s29j4fhsmzodl9f7kn2z.png)
=117.28km
in nearest 10 it is 117km
the total distance Rosie had travelled by the end of 10 days is 117km.